Action Points

Note that in another study, measuring vitamin D levels before thyroidectomy probably won't help determine if a patient will develop hypocalcemia after surgery.

MedPage Today has been reviewing this year's highlights in vitamin D research in several articles. This installation acknowledges a case of an iatrogenic overdose of vitamin D (a 10-dose course of 600,000 IU injections), whether the vitamin plays a role in inflammation, its lack of efficacy as a predictive tool to determine which thyroid surgery patients will go on to develop hypocalcemia, a possible role in weight loss, and its lack of impact on clinical depression.

Iatrogenic Overdose

A vitamin D overdose could manifest as persistent vomiting, as was the case for one woman who was prescribed a 10-dose course of 600,000 IU injections following knee surgery.

By the time the 45-year-old woman presented to Sir Ganga Ram Hospital in New Delhi, she'd had recurrent vomiting, abdominal pain, and constipation for a month and a half.

When they looked at her medical records, they found that she'd been prescribed intramuscular shots of cholecalciferol (Arachitol) 600,000 IU every other day for 10 doses following a knee surgery 2 months earlier.

They checked her vitamin D levels, and they were way above the 20 ng/mL considered sufficient. In fact, they were nearly eight times higher, at 150 ng/mL.

She was treated with IV fluid, diuretics, and calcitonin. Over the next 15 days, her levels returned to normal. She was discharged with orders for a low-calcium diet and good hydration.

It's not clear how prevalent vitamin D toxicity is, the researchers said, but with increasing screening for sufficiency, it could be more common now than it has been in the past.

They urged clinicians to suspect vitamin D overdose in patients who have persistent vomiting and hypercalcemia, especially when parathyroid hormone levels are normal.

Two vitamin D studies from Ireland made headlines in the same week this year in March: One looked at the vitamin's role in inflammation, and the other on how it impacted calcium levels after thyroid surgery.

While its musculoskeletal benefits are clear, vitamin D's role in inflammation and immune system modulation is less so.

Mary Ward, PhD, of the University of Ulster in Coleraine, Northern Ireland, and colleagues looked at data on 957 older hypertensive patients (mean age 70) from an Irish cohort study.

They found that patients with vitamin D deficiency had higher levels of the inflammatory cytokine IL-6 and C-reactive protein (CRP) than those who had sufficient levels of the vitamin.

A more inflammatory immune profile could be a risk factor for chronic conditions including heart disease, they reported online in the Journal of Clinical Endocrinology and Metabolism.

Although their findings need to be confirmed in larger studies, Ward said, ensuring that older patients "have optimal vitamin D levels may be a way to boost [their] immune function," and potentially stave off chronic disease.

Although exact estimates vary, it's not uncommon to develop transient hypocalcemia after having the thyroid removed, usually because of a concurrent drop in levels of parathyroid hormone (PTH), which plays a key role in calcium metabolism.

Some have speculated that an underlying vitamin D deficiency might increase the risk of falling calcium levels after surgery, but little research has been done.

Patrick Sheahan, MD, of South Infirmary Victoria University Hospital in Cork, Ireland, and colleagues looked at data on 121 patients who had thyroidectomy. About a quarter subsequently developed hypocalcemia.

They found no links, however, between vitamin D levels before surgery and later development of low calcium.

That said, clinicians shouldn't discount the fact that vitamin D may be able to help restore calcium levels in these patients after surgery, they wrote.

Anne McTiernan, MD, PhD, of the Fred Hutchinson Cancer Research Center in Seattle, and colleagues randomized the women, all of whom were given a dietary intervention, to either 2,000 IU oral vitamin D3 daily or placebo.

Although there were no differences between groups by the end of the study in terms of weight loss or other metabolic parameters, they found that within the vitamin D group, those who had achieved sufficiency lost significantly more weight than those who hadn't (8.8 lbs versus 5.6 lbs, P=0.05).

These women also had greater losses in waist circumference and body fat, McTiernan and colleagues reported.

It's still not clear exactly how vitamin D is involved in obesity. There's no way to tell if becoming vitamin D sufficient causes further weight loss, or if better weight loss led to improvements in vitamin D status.

But McTiernan and colleagues wrote that their study can help inform future trials that may be able to detect greater effects -- and can further tease those effects out -- if clinicians individualize supplementation so that more patients become vitamin D replete.

No Effect on Depression

Depressed patients won't get any relief from vitamin D supplementation, a new meta-analysis found.

However, when looking specifically at patients who had clinically significant depressive symptoms or depressive disorder, the researchers found that there did appear to be a moderately significant effect of vitamin D supplementation on symptoms.

In a press release, the researchers noted that further work should be done on whether vitamin D adds to improvements when patients are also on antidepressants.

They also noted that supplementation may work when depressed patients have an actual deficiency in vitamin D, but more studies are needed.

It seems there's at least one new study of the vitamin published every day, and in the Vitamin D Blog, MedPage Today will monitor that steady stream, offering our take on clinical implications -- or limitations.

Have a tip on a vitamin D study? Email Kristina Fiore at k.fiore@medpagetoday.com. You can also catch our vitamin D feed on Twitter, @vitaminDblog.

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